This invention relates to data base searching and in particular to methods and system therefor employing optical techniques.
I have previously proposed an associative optical memory system in my GB Patent Specification 2161263B (U.S. Pat. No. 4,701,879), the contents of which are incorporated herein by reference.
According to claim of 1 GB 2161263B there is provided an associative optical memory system comprising an optical imaging system, in the form of a matched optical holographic filter, and, coupled thereto, a digital computing system including a memory, and wherein in use for searching the computer system memory for occurrences of an item the computing system controls the input and Fourier transform planes of the filter and a coherent light source for parallel optical processing of the memory content, and the output plane of the filter provides information to the computing system as to the location in the memory of the occurrences of said item.
As discussed in my copending GB Application 8903997.8 Ser. No. 2228601A) (R W A Scarr 39) the contents of which are also incorporated herein by reference, the increasingly widespread use of mass optical and magnetic means for storing un-indexed data means that there is a requirement to search large amounts of information in periods of not more than a few seconds. Electronic systems such as CAFS (Content Addressable File Store) enable magabytes of data to be searched against a Key in periods of less than ten seconds. Data bases of the gigabyte order require search times rather shorter than those currently available by electronic means. Optics provide a potential means, probably in combination with electronics, of searching in parallel with a view to reducing the net search time. The present invention is concerned with a content addressable memory as in GB 2161263B and GB 8903997.8 and where the required information is, rather than what it is. The actual retrieval of the information once found within the mass of data is a secondary operation which could use optical techniques, although it is presently considered that it is more likely to use electronic techniques or a combination of optical and electronic techniques.
Currently data is stored largely in the digital form of 8 bit or octet such as an 8-bit ASCII code but one can anticipate an increasing need, in the future, to treat documents in facsimile form or in some mixed mode with hand-written comments, logos, diagrams etc. being distinguished from coded text but linked together within the storage medium. CAFS involve a few parallel channels processing serially strings of binary coded characters and are unsuited to the recognition of graphical material. There are, of course, optical and electronic designs for pattern recognisers that provide a more general approach than CAFS does.
Ideally any pattern recogniser should be able to recognise a pattern independently of translation, scale and rotation. The use of a Fourier transform enables patterns to be recognised independently of translation, and optics provides a virtually instantaneous means of Fourier transforming large amounts of data in parallel. An optical Fourier transform with some scaling means provides a means of combining scaling and translation. Rotation is a more difficult problem. Our co-pending Application GB 8903997.8 was concerned with a translation--independent optical matched filter (correlator) using real-time holographic recording and recognising patterns of known semantic content (i.e. text), especially coding and recognising coded characters. The holographic optical correlator of GB 8903997.8 is a spatially invariant correlator.